The present invention relates to an aircraft, and more particularly to a landing gear support assembly for an aircraft.
Aircraft landing gears on some aircraft are moveable between a deployed position (adopted for take-off and landing) and a stowed position (adopted during flight). The landing gear is often, therefore, retractably mounted on a landing gear support assembly located in the aircraft wings. The landing gear support assembly typically includes a pintle support assembly for holding a pintle on which the landing gear is rotatably supported. The landing gear support assembly is usually arranged such that the landing gear, when stowed, is mainly contained within the notional envelope defined by the wing. In recent years however, aircraft have been designed with increasingly thinner (lower thickness-chord ratio) wings. The arrangement of some existing landing gear support assemblies is such that the landing gear cannot be contained within these relatively thin wings. By way of example, in one such arrangement the pintle is supported on the shear centre of the support structure below the support structure, thus requiring a certain depth of wing.
It is also desirable for the landing gear support assembly to transfer the loads from the landing gear into the aircraft structure in a manner such that the landing gear support assembly, and the structural components surrounding it, need not be unduly heavy. In an aircraft of the prior art, the spar associated with the landing gear support assembly has a locally increased cross-sectional area to cope with the high loads in the region of the landing gear support assembly. Such a spar is therefore more difficult to manufacture than is desirable. Also it would be desirable to reduce the mass of the spar and/or the landing gear support assembly.
Moreover, the general desire to reduce mass in aircraft design has caused there to be a motivation to manufacture an increasing number of aircraft components from composite materials. However, many existing landing gear support assemblies are unsuitable for use with such composite materials due to their geometry and nature of the loads occurring during use.
U.S. Pat. No. 4,392,623 describes a landing gear support assembly in which a pintle is supported at one end on the rear spar and at the other end on a landing gear support beam, which extends from the rear spar to the fuselage. The provision of a landing gear support beam that extends from the rear spar to the fuselage significantly adds to the bulk and mass of the wing. Furthermore, the arrangement illustrated in U.S. Pat. No. 4,392,623 would not be suitable for manufacture in composite materials, as a result of the complicated geometry required of the various moving components, without significant modification that would probably add further weight.
U.S. Pat. No. 6,679,452 acknowledges and illustrates (in FIG. 2 of U.S. Pat. No. 6,679,452) a prior art landing gear support assembly, in which pintle supports are located on a gear rib (referred to in U.S. Pat. No. 6,679,452 as a trunnion support beam) and the rear spar respectively. Although this arrangement presents a solution different from the arrangement disclosed in U.S. Pat. No. 4,392,623, the landing gear support assembly acknowledged in U.S. Pat. No. 6,679,452 suffers from various disadvantages. During use, significant loads are transferred through the gear rib and the rear spar pintle support, directly into the rear spar at positions close to each other, thereby creating a high stress concentration in this region of the rear spar. Thus, it is necessary to locally increase the thickness of the rear spar, thereby increasing the weight of the rear spar and production costs. Furthermore, the prior art described in U.S. Pat. No. 6,679,452 is of limited application when considering how to design a predominately composite material wing box, because it is particularly difficult to manufacture a sufficiently robust rear spar pintle support using composite materials, as a result of the need to provide a pintle support directly on the rear spar. In addition, composite materials can be relatively inefficient at redistributing the loads within the structure. A landing gear support assembly of the arrangement disclosed in U.S. Pat. No. 6,679,452 would, therefore, generate even higher stress concentrations in the rear spar, if manufactured using composite materials.
FIG. 1 illustrates a further landing gear support assembly representative an arrangement used in the prior art on a Lockheed L-1011 TriStar aircraft. In that arrangement a cantilever beam, in the general form of a gear rib 101, is mounted on and supported by the rear spar 103. Connecting rods 105 extend between the cantilever beam and the fuselage. The loads transmitted through the pintle supports 107, 109 during use, are therefore spread between the rear spar and the fuselage, via the cantilever beam and connecting rod arrangement, respectively. This arrangement may therefore present a lower mass solution than the prior art arrangements described above. However, the pintle of the landing gear assembly is located on the underside of, and in the plane of, the gear rib. The particular arrangement of the pintle is such that the invention is not readily applicable to an aircraft having relatively thin wings as the notional envelope defined by the wing must be of a sufficient thickness to wholly contain the landing gear assembly in the stowed position. For example, the provision of the connecting rods restricts the possible positioning of the landing gear assembly when in the stowed position. Furthermore, the longitudinal axis of the pintle is not located in the same plane as the neutral axis of the rear spar. This may lead to a significant stress imbalance in the landing gear support assembly.
It is an object of the present invention to provide an improved landing gear support assembly that mitigates at least some of the above-mentioned disadvantages of the prior art.